Can this PT and OT work for a 36W?

[jmilch]

Fore reference, they were pulled from a Hammond organ.

Amp model AO-63

Here is the picture with identifying numbers.

I'd like to do a basic 18W Lite II but with 4 EL84 ouputs.

Would this iron be sufficient?

[Phil_S]

I was able to find that the original tube set is 2x 7591, 2x ECL86, EZ81, and 4 preamp tubes. This is more than adequate for the filament supply requirements and overall current supply for the B+.

Do you have any idea what the HT secondary voltage is? This is easy to find out. You will need to plug it in. Use a power strip with an on-off switch. Take an ordinary power cord with plug on one end and pigtails on the other. Attach the pigtails to the primary supply wires on the PT using wire nuts. (It may help to screw the PT to a plank of wood to stablize it, but I just stand them upside down and don't worry about it.)

Turn off the power strip. Plug in the power cord. Attach the meter on A/C scale to the two HT secondary wires. Turn on the power strip and you'll get your answer. Figure there is about a 5% load loss from that number. If you see 600V (that's 300-300) figure you will see a bit less than that in circuit (maybe 290-290). That's about where you want to be with it. Post results if you are unsure.

[Phil_S]

I have no idea about the output transformer. You should test for turns ratio. here: http://www.radioremembered.org/outimp.htm

[jmilch]

I was able to find that the original tube set is 2x 7591, 2x ECL86, EZ81, and 4 preamp tubes. This is more than adequate for the filament supply requirements and overall current supply for the B+.

Do you have any idea what the HT secondary voltage is? This is easy to find out. You will need to plug it in. Use a power strip with an on-off switch. Take an ordinary power cord with plug on one end and pigtails on the other. Attach the pigtails to the primary supply wires on the PT using wire nuts. (It may help to screw the PT to a plank of wood to stablize it, but I just stand them upside down and don't worry about it.)

Turn off the power strip. Plug in the power cord. Attach the meter on A/C scale to the two HT secondary wires. Turn on the power strip and you'll get your answer. Figure there is about a 5% load loss from that number. If you see 600V (that's 300-300) figure you will see a bit less than that in circuit (maybe 290-290). That's about where you want to be with it. Post results if you are unsure.

When I get home I will throw it together and let you know. Thanks for the tip on testing!

[Freddy]

With a push pull pair of 7591s, the OT is probably in the 6-7K range. Good for 6v6, 6l6, 7868, 7591, and some others. The turns ratio test will give the best informations though.

[Shrapnel]

Freddy's in the ballpark with the OT tranny primary impedances. Most 7591 circuits call for 6k6 primary... I pulled a OT out of a Lowery organ that had 7591s in it 6k3 primary (within 10% of a 6k6) and 16R out.

With about 400v on the plates of those 7591s, you should see about 36W "fixed" bias, slightly less cathode (although book specs give a higher impedance tranny & 450v for the plates for 28W out.)

Use a std 18watt PI (as used with EL84s) and the 18watt pre of your choice.

Of course, you can get a OT from Matt over at MPS that would be big enough, and can ask for one with the proper primary impedance... just give him about 3 weeks or so as long as he has the materials.

[Snapcase]

6K6 OT primary is ok for a cathode biased EL34 pair as well.

7591 and EL84 are driven easy with not so big signal. Maybe the driver should be tweaked a bit for a higher gain if using EL34s.